1. Field of the Invention
This invention relates, in general, to electrical bushings and, more particularly, to fluid-filled electrical bushings for connecting transformer windings to dielectric fluid-filled bus ducts.
2. Description of the Prior Art
Connecting the electrical winding of a transformer, reactor, regulator, etc., to another electrical apparatus or conductor usually involves an electrical bushing assembly. The bushing is attached to the transformer case with its internal end connected to the winding and its external end connected to the conductor. In some applications, the conductor is housed in a duct which is filled with a dielectric fluid, such as oil, or a gaseous dielectric, such as sulfur hexafluoride, under a predetermined pressure.
Bus-conductor ducts present specialized problems in making the electrical connection between the bus-conductor and the winding lead of the transformer. It is difficult to contain the oil within the bus duct since the oil, when subjected to an electrical arc, may give rise to an explosion. Similarly, the sulfur hexafluoride gas used in pressurized bus ducts has a tendency to seep into the fluid-filled bushings contained therein which, again, may give rise to a pressure induced explosion. Although pressure sensing devices, such as pressure switches, have been used to detect increased pressure within the bushing caused by the above-named factors, such devices are generally inefficient since they must be set to operate at a pressure higher than the pressure caused by normal temperature excursions of the dielectric fluid within the bushing.
Thus, it would be desirable to provide an electrical bushing wherein the risk of an explosion is substantially reduced. It would also be desirable to provide an electrical bushing which includes means for indicating an abnormal internal pressure condition caused by arcing, expansion of the dielectric fluid within the bushing as would occur as the result of excessive heating, or the introduction of pressurized gaseous dielectric into the bushing itself.